Hand trucks typically have a frame for supporting a load which is to be moved, a pair of wheels at the lower end of the frame and hand grips at the upper end. The operator holds the frame in an inclined position and pushes or pulls on the hand grips to maneuver the load from one location to another.
The traditional hand truck construction is well suited for moving objects along a floor or other level surface but becomes more difficult to handle when the load must be moved up or down stairs, across a curb or along some other discontinuous surface. During portions of such travel, it is the frame rather than the wheels that contacts the underlying surface. This creates high friction and resistance to movement of the truck and can also damage flooring, carpets or the like. Movement of the truck wheels off of the edges of stair treads also tends to generate jarring movements of the truck which complicate the operator's task and which can damage fragile loads.
These problems can be avoided by equipping the truck with a pair of endless belt track assemblies each of which extends backward for a distance along the underside of the frame behind a separate one of the ground wheels. The belt bears against a series of rollers situated along the underside of the track assembly and carries the weight of the truck during periods when the ground wheels are out of contact with the stair or other underlying surface. Prior U.S. Pat. Nos. 4,290,618 and 2,193,283 disclose examples of such track assemblies for hand trucks. Prior U.S. Pat. No. 4,136,888 discloses another form of track assembly of this kind on a transport chair for invalids rather than on a hand truck. U.S. Pat. No. 2,620,041 describes a large motor driven track assembly designed to replace the ground wheels rather than to supplement such wheels.
The arrangements of rollers, pulleys, guideways and the like which have heretofore been used to support and position the endless belt are not optimal from the standpoint of reducing frictional resistance to belt movement and can be prone to jamming. In some cases, the belt rides against fixed surfaces of the assembly that create high friction. Support rollers in some cases are situated in constricted spaces that can accumulate debris which increases friction and may cause jamming or binding. In some prior constructions, the belt is deliberately chosen to be larger than its guideway apparently in an effort to minimize frictional resistance. A loosely fitted belt of this kind can hang down during normal travel of the truck creating a loop which can snag on object along the route of travel. The hanging loop also presents a sizable opening through which debris can enter the roller mechanism.
The present invention is directed to overcoming one or more of the problems discussed above.